[FFmpeg-user] ffmpeg slowly get out of sync

[Luo Xin]

Yes, that's my first guess, and I try to fix it with "-async num" or 
"-vsync 1", I get the idea from:

http://lzone.de/cheat-sheet/ffmpeg


while for my case, it didn't related with different clock crystal 
(actually the two stream comes from same capture device), it is because 
I incorrectly use very different time stamp:

Input #0, alsa, from 'hw:3':
   Duration: N/A, start:*1479202954**.916662*
Input #1, video4linux2,v4l2, from '/dev/video2':
   Duration: N/A, start:*31.451263*

I guess it related with the accuracy of float calculation during time 
stamp scaling/resample, maybe Carl could give the reason?

Thanks,
Luo Xin

On 2016年11月18日 12:37, Reuben Martin wrote:
> On Wednesday, November 16, 2016 7:59:44 PM CST Luo Xin wrote:
>> - capture video from v4l2 device
>> - capture audio from alsa device
> The drift is going to happen to a certain extent no matter what. You are
> sourceing from two separate pieces of hardware that do not share a common
> hardware clock crystal.
>
> -Reuben
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